In it, Verizon points out that the various claims T-Mobile made to defend its merger with AT&T seem to contradict the reasons it is now giving the FCC for blocking Verizon's acquisition of nationwide AWS spectrum from four cable operators.

"T-Mobile cannot continue to have it both ways, and its attempts to extract competitive advantages during the transaction review process should be disregarded," Verizon said.

T-Mobile is one of the few operators to ask for an outright block of the transaction, claiming it will concentrate too much spectrum in the hands of a single company. It has not yet filed a rebuttal to Verizon's latest comments.

During the government’s review of its merger with AT&T, T-Mobile was forced to frequently defend the deal against accusations it would be detrimental to competition. But it has found itself on the other side of the fence after the merger failed, even joining the Rural Cellular Association, a vocal opponent to the AT&T buyout.

Verizon attempts to discredit T-Mobile's opposition to the AWS deal by detailing its change in course to the FCC.

It pointed out that T-Mobile testified during the AT&T transaction that the U.S. wireless industry would remain "fiercely competitive" if its merger with AT&T closed – a transaction that would have eliminated a major competitor – but later said that if Verizon was allowed to buy more AWS spectrum, there would be "serious harm to competition” and to consumer welfare.

"Despite its earlier claims that the combination of two top-four facilities-based providers would have no impact on competition in a fiercely competitive marketplace, T-Mobile now argues that the acquisition of a discrete block of spectrum – and only spectrum – by a carrier that needs it to meet its customers’ escalating demand for mobile services will 'serious[ly] harm' competition," Verizon said.

T-Mobile is not the only operator that has asked the FCC to stop the AWS deal from moving forward. MetroPCS is also on board, and Sprint has requested the agency "carefully review" the transaction, though it has stopped short of asking it be blocked.

Sprint, DirecTV and seven other groups asked the FCC this week to delay its review of the Verizon spectrum sale, claiming difficulties accessing important documents about the deal. The FCC has not said whether it will grant the request.